Aqueous dispersions and emulsions of water-insoluble polymers for use as paints, sealants, caulks, adhesives or other coatings are well-known, widely-used articles of commerce. The effectiveness of the dispersion in forming a film after the polymer dispersion has been deposited upon a surface depends upon the glass transition temperature of the dispersed polymer and the temperature at which the film is allowed to form.
Coalescent aids have been used in such aqueous dispersions to soften, i.e., plasticize, ideally temporarily, the dispersed polymer phase and facilitate the formation of a continuous film with optimum film properties once the water has evaporated. In addition to increasing the ease of film formation, the coalescent aid also promotes subsequent improvements in film properties by coalescing the water-insoluble polymers and forming an integral film at ambient temperatures. Without the coalescent aid, the films may crack and fail to adhere to the substrate surface when dry.
Coalescent aids, also known as coalescing solvents or simply coalescents, are particularly helpful in assisting in film formation at temperatures below the glass transition temperature of the dispersed polymer.
Various alcohol esters and ether alcohols have been proposed for use as coalescent aids. For example, in U.S. Pat. No. 4,131,580 Emmons et al. disclose water-based coating compositions based on vinyl addition polymers of monoethylenically unsaturated monomers which comprise dicyclopentenyl acrylate and/or dicyclopentenyl methacrylate as a coalescent aid. In U.S. Pat. No. 4,141,868, Emmons et al. suggest certain ester-ether compounds be used instead.
Two of the more widely used coalescent aids are ethylene glycol monobutyl ether (Butyl CELLOSOLVE®, Dow Chemical) and 2,2,4-trimethyl-1,3 pentanediol monobutyrate (TEXANOL®, Eastman Kodak). While Butyl CELLOSOLVE® and TEXANOL® are useful in facilitating film formation of coatings formulated with water insoluble polymers with high glass transition temperatures and are even useful in facilitating film formation of coatings with low glass transition temperatures if they are being applied at a temperature that is lower than ambient temperature which is higher than the glass transition temperature of the coating, they are relatively volatile and, as a result, are currently classified as VOCs (volatile organic compounds) in the US.